Hello, Though I know absolutely nothing about these clubs I do know that making true circles is a very easy task (something I learned in the Boy Scout years ago) by simply attaching a piece of flint to the side of a round pointed stick, making a small indent to place the point in and and rotating it by rubbing it between your hands just like you're trying to star a fire. The size of the circle just depends on the diameter of the stick you use. If you are real industrious, you can use a bow to turn the stick.
Robert
PS
I forgot to mention, you carve a flat spot on the side of the pointed stick where you are going to mount the piece of flint or what ever sharp item you are going to use.